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What makes snow on the wings during take off so dangerous?
What is the cause of the widely known danger of snow on the wings of the airliner? Why does it require deicing before taking off?
I cannot believe it just makes the plane too heavy, and it is not obvious if it could alter the wing shape for this to be a problem. Control surfaces may not move as commanded? Possible shape and balance differences between left and right sides when that snow starts leaving the wing?

SK 751 is an example of what can happen (though specific to tail-mounted engines).

Snow and ice on the tail can actually be heavy enough to tip the plane over onto its tail, plus the wings and fuselage have a very large surface area so that weight actually does add up.  That being said, the larger dangers are the aerodynamic effect from making the wing surface uneven and rough which increases drag and reduces lift significantly (I'm sure that someone will expand with a more detailed and technical answer, but this is it in a nut shell.)

On Skeptics.SE: Can a sandpaper-thick layer of ice reduce lift by 30 percent and increase drag up to 40 percent?

Related: http://aviation.stackexchange.com/questions/25367/what-phenomenon-causes-the-increase-of-drag-with-rain

If you've ever touched an aircraft wing with your hands, you'll notice they're exceptionally smooth. Under a magnifying glass, the effects of snow and ice on the wing's shape become very obvious.

Even the seams and rivets on the wing cause drag. Older Mooneys used flush rivets to reduce drag and improve speeds. One of the ways modern aircraft like Cirrus and Lancair improve performance is to use composite wings with no rivets or seams. As kevin said, wings are exceptionally smooth, but the difference between an aluminum wing and composite is striking and accounts for a lot of the efficiency of composite airplanes.

Also related: Why are dirt and bugs on an aircraft so bad?

it is not obvious if it could alter the wing shape for this to be a problem
It may not be obvious but it is so.
Plain old snow will just blow off as soon as the plane picks up speed, but if the wing was above freezing when the snow first fell on it, the snow will probably conceal a layer of rough ice, which will not blow away.
Anything adhering to the wing surface will change the lift force. According to this article even a thin coating of ice can disrupt an airfoil's boundary layer airflow, causing a premature aerodynamic stall and dramatically increased functional drag.

Excellent answer, +1. You might expand it by saying that during and shortly after liftoff the wing is pushed to its limits, which are greatly affected by small disturbances especially near the nose. See here or here for the influence of bugs and rain on glider wings which pose a very similar situation.

Another classic example is that even a thin layer of frost (not ice) can destroy a third of the wing's potential lift, significantly increase stall speed (and thus safe liftoff and approach speed), etc.; and an equally large danger is the pilot(s) have no way of knowing how much effect today's snow/ice/frost is having at any given time-its much easier to simply deice and move on.


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Crop dusting regulations in the US
What are the regulations regarding crop dusting and flying low over private property. Do they have to file a flight plan and is there a way to make your private property a no fly zone?

The first part of your question is probably answered in the dupe that @ratchetfreak linked to, but the second one about a private no-fly zone isn't. You might consider making that the main question here.

I agree with the previous comment. You generally can NOT make your property a no-fly zone, as all airspace is part of the US Airspace System (imagine every land owner declared no-fly zones!). That is, of course, if we're talking about the US here, which I assume. If your quest is to prevent a crop duster overflying your property, you'll probably be more successful with other approaches (i. e. not trying to make it a no-fly zone). Perhaps talk with your zoning board, the state, etc., but here as well: crop dusting is usually done in agricultural areas, where crop dusting is allowed.

To answer your questions:
A crop duster does not have to file a (normal) flight plan. They do have to file a special "operations" plan if they are going to be spraying chemicals. Notice of the intended operation must be given to the public by some effective means, such as daily newspapers, radio, television, or door-to-door notice. A plan for [the spraying] operation must be submitted to, and approved by appropriate personnel of the FAA Flight Standards District Office having jurisdiction over the area where the operation is to be conducted. The plan must include consideration of obstructions to flight; the emergency landing capabilities of the aircraft to be used; and any necessary coordination with air traffic control.
All aircraft must maintain a height of at least 500 feet above ground or objects on the ground, like a house. (Minimum Safe Altitude) A crop duster can go below this height only to operate to apply chemicals and for no other reason. The exact text of the exception reads as follows: "No person may operate an aircraft over a congested area below the altitudes prescribed in part 91 of this chapter except during the actual dispensing operation, including the approaches and departures necessary for that operation."
You cannot prevent someone from flying over your house.
If someone is flying over your house at less than 500 feet, you can file a complaint with the FAA by calling (703) 230-7664. Please observe the following:
• Identification - Can you identify the aircraft? Did you record the registration number which appears on the fuselage or tail? (On U.S. registered aircraft, that number will be preceded with a capital "N".)
• Time and Place - Exactly when did the incident(s) occur? Where did this happen? What direction was the aircraft flying?
• Altitude - How high (low) was the aircraft flying? On what do you base your estimate? Was the aircraft level with or below the elevation of a prominent object such as a tower or building? Did you obtain photographs? Are there any witnesses who could confirm your estimate - do you have their names, addresses, telephone numbers?
• Supporting Evidence
• Witnesses, Police
• Photographs

The FAA allows lower flight for crop dusters when needed and safe, though.

Sorry, I have to downvote. "All aircraft must maintain a height of at least 500 feet above ground" is positively wrong. (and, I mean, think about it logically, have you ever seen a crop duster flying at 500 AGL? They fly low, pretty low, which is actually a danger factor for the pilots, and if they were really flying at 500 AGL or above, it would be a danger for the neighborhood, as the pesticide would reach unintended properties. I also believe that a VFR flight plan is needed, but would have to look into that again. So, given that I have explained myself, I think I'm allowed to downvote.

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Can helicopters perform the Split S maneuver?
In the animation movie "Planes 2" we see the helicopter (Blade character) performing first a 180° roll (getting inverted chassis up and rotor down) and then the U-shaped half loop down into the normal orientation. From Wikipedia it looks like the Split-S.
Are helicopters actually capable of doing this? The concerns are

An inverted wing still may provide a lift upwards, but the inverted rotor will pull downward. Hence the inverted orientation seems risky.
Wings provide air support while making the sharp U-turn. Can the helicopter rotor do the same?

If a helicopter would manage this figure, would it trade altitude to speed as the fixed wing planes do?
If the model is important, the helicopter looks somewhat like Augusta Westland.

Related: Why aren't there more helicopter aerobatics at airshows?

Related: What is required to be an “FAA-qualified helicopter aerobatics pilot”?

Here is a helicopter performing a split S. And rolls, loops ...

@Steve That's not a split-S, is it? It starts from a near-vertical climb, whereas the split-S starts from level flight.

@DavidRicherby Details... :)

Yes, but you need a rigid head.
A rigid head does not have any hinges, instead, the blades flex up and down.
Wings don't know or care if they are upside down or right way up, indeed, most helicopter blades are symmetrical.  It only cares how much airflow there is and at what angle it hits it.
Here's an EC-120 performing a split S and a Lynx showing what's possible.
Perhaps the best around is Chuck Aaron, displaying for Red Bull.
Here, Dennis Kenyon shows about as good as it can get with a semi-rigid head.  He gets close to inverted but never actually flips over.

"Wings don't know or care if they are upside down or right way up" although this is true, helicopters cannot maintain inverted flight because the rotary wing can't have negative pitch, where as even an airplane with an asymmetrical wing can fly inverted because it can have negative pitch.

@rbp: Right, but you don't need to be able to maintain inverted flight to do a split S, since you're only inverted momentarily.  You can even do a split S while pulling positive Gs throughout, if you do the initial inversion with a half barrel roll rather than the traditional half aileron roll.

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Is there a Flights API to get flight information months in advance?
I hope I am at the right place here. Asking this at Stackoverflow is not allowed (off topic)
I want to be able to plan flights in the future. (6-12 months ahead) I only know the Flights ID like LH2014. All I want is to get the departure/arrival airport and times.
Do you know of any API or fresh database?
If I am booking a flight 6 months in advance I will get all the information. So it should be possible. Or is this the data from the day I booked the flight?
I tried few APIs like flightaware or flightstats, but they can only deliver data for max. 72 hours in advance, not 6 months.

I am afraid that this is off-topic also here. you might be better ask in chat. Nevertheless, 6 months might be too much as usually airlines change their timetables seasonally.

I disagree, I feel that this question is on-topic for us.

no problem, thanks anyway :)

A similar question was asked on Stack Overflow: https://stackoverflow.com/a/2899086/178673 (and marked off-topic, but it did have some answers)
When you are booking a flight, you are typically providing more information than just the flight number, in fact, the query is usually "here is my date/time and arrival/departure information, what is available?"
You are providing the departure date (or range) and arrival date (or range), as well as the city-pairs, and when you have that data you can use the API from FlightStats to find out the list of flights: https://developer.flightstats.com/api-docs/scheduledFlights/v1
If you just knew the flight number, you could use the API call for "Scheduled Flight(s) by carrier and flight number, departing on the given date. /v1/json/flight/{carrier}/{flightnumber}/departing/{year}/{month}/{day}, but again, you still need something to put in as either the departing or arrival date.
Programmatically, perhaps if it didn't return a hit for the date you specified, you could search on x days of either side of the date.  For example, October 19, 2014 didn't return a hit for LH2014 (I know this is a daily, Monday-Friday flight), and the API would return that it didn't hit, so then we (arbitrarily in this example) check two days on either side
Psuedo-code example:
day = 19
/v1/json/flight/LH/2014/departing/2014/10/{day-2}
/v1/json/flight/LH/2014/departing/2014/10/{day-1}
/v1/json/flight/LH/2014/departing/2014/10/{day+1}
/v1/json/flight/LH/2014/departing/2014/10/{day+2}

And find out that it is scheduled on the 17, 20 and 21 of October and that it flies MUC-DUS, in an A319/20.
So, the API isn't going to do all the work for you, but you could probably wrangle the API to give you the information you want in a format you want.  With some built-up logic around the question you're really trying to ask and multiple API calls (Is this flight number available on this date and what are the city-pairs, and if it's not available what date(s) is it available?).
Hope this is helpful. :)

Web archive link to deleted stackoverflow thread: https://web-beta.archive.org/web/20161104004954/http://stackoverflow.com/questions/2895064/web-based-flight-status-api

This (link) is a working link of the deleted thread on the web archive.


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Why are CJ2+ Anti-Ice & De-Ice Systems separately controlled?
Why are the CJ2+ anti-ice and de-ice systems separately controlled? Wouldn't it be easier for both systems to be controlled with one button/switch (minimize chance of error from occurring)? Are there any aircraft that have the two systems controlled by one button/switch that would be activated as soon as ice is detected?

Because they do two different things.
To quote FlightSafety's CJ2 Pilot Training Manual:

Anti-ice protection systems are incorporated into wing, engine
  components, windshield, pitot-static, and angle-of-attack systems, and
  pylon ram-air scoops.  These systems should be activated prior to
  entering icing conditions.
The tail deice system consists of pneumatic boots on the horizontal
  stabilizers.

Basically, anti-ice is used to prevent ice from forming in the first place on the protected surfaces of the aircraft.  This is done where it would either be "bad" to have it form in the first place (pitot-static, angle-of-attack, etc.), or where it would be "bad" to have the ice come off after it has formed (and then go through an engine, etc.).
Deice is used to remove ice after it has formed.  In this case it is used on the tail which a) isn't critical if it has a little ice, and b) the ice can be broken off after it has formed and it will just fly off the back of the airplane without damaging anything.
Since they serve two different purposes (and protect different parts of the aircraft), there are two different controls/switches.

think of it from an MEL (Minimum Equipment List, manufacturer/governing body approved manual for working equipment & non-working equipment installed on aircraft) stand point if you have 1 switch controlling both systems and the fault lies within the switch, and you don't have a spare (or mx personnel) at the outstation with known-icing conditions probably means you aren't taking off. Yet if you separate systems you might be able to get airborne and play dodge cloud then, remaining clear of known icing.
As for specifics to that aircraft I am not privy as I don't fly it.  Other aircraft that are controlled by logic and automated are pretty self explanatory if you understand the nature of its function.

The reason I brought up the question is because if the plane enters icing conditions and say the anti-ice system for the wings is engaged but the deice system for the tail is forgotten about it could cause the plane to become difficult to control and/or an increase in stall speed. I would think having both systems controlled by one button/switch would minimize a possible human error from occuring.

I see what you are asking... On the EMB145 it has separate buttons for Wing/Stab and each Engine has lip anti-ice on their respective bleeds.  They are all automatic so there is nothing to do unless an EICAS msg is presented.  On the EMB145 the overhead panel is designed in such a way that if the panel is not dark then something is open or wrong.  If there something wrong in this case then we run the appropriate QRH checklist according to the msg.  Normally all buttons are selected and it will function based on detectors then.

@mvermef "hey are all automatic so there is nothing to do unless an EICAS msg is presented" except on the ground with visible moisture and SAT <= 10C, in which case you'll manually turn on the engine lip a/ice until your after takeoff flow. (EMB-145)

@casey yep absolutely correct...

@mvermef What you say makes sense. Thank you for giving me the info about the EMB-145. Smaller planes with anti-ice and de-ice systems are advised to exit icing conditions as soon as possible.The thing about my question is that (according to research) sometimes pilots don't detect the icing conditions right away or they don't realize the severity of the conditions. It doesn't take long for ice to accumulate and effect the aerodynamic stability of a plane. I was wondering if the CJ2+ design was influenced by the belief in "ice bridging".


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Do rotorcrafts like helicopters have autopilots?
Years ago, I had the opportunity to board a Bell 407 for a long distance flight and put every question related to helicopters that crossed my mind to the pilot when we were forced to land due to visibility issue and also while we refueled.
I realize now that I've missed something important: do rotorcraft including helicopters have autopilots like fixed wing aircraft do, or is that ruled out due to their peculiar flight mechanics?

Googling suggests there are many manufacturers of autopilots for helicopters.

"Long distance" and "helicopter" don't quite belong to the same sentence ;)

Yes, helicopters can be fitted with autopilots. Some are very simple, others are quite advanced. The more advanced ones can, for instance, follow a pre-programmed route, climb/descent to a pre-selected altitude, fly an ILS approach, perform a go-around automatically.
They are not ordinarily found in small helicopters due to cost and lack of necessity. All modern offshore helicopters that I've encountered have them and they are used extensively. Usually they are engaged shortly after take-off and disengaged shortly before landing.

The first half of this is a good answer. The rest seems to diverge from the topic of this particular question though.

Updated to remove diverging additional info

This Article about HeliSAS seems to elude to the fact they can and certified systems exist. The specs of this helicopter list it as having

...Airbus Helicopters’ advanced Helionix® avionics suite with a 4-axis
  digital autopilot


text:
Can an airport without an FAA controlled tower have their own tower and controllers?
Can an airport not eligible for an FAA tower and controllers choose to fund their own air traffic control tower? Can that airport require pilots to taxi, approach, land, and take off according to their tower's instructions?
If so, are there requirements for the controllers in terms of certification, or can they hire anyone they deem suitable for their airport? Do they have to coordinate with the FAA or air traffic control system in some special way?

Yes, in fact there are a number of Non-Federal Control Towers (NFCT) in the United States.  These are NOT the same as Federal Contract Towers (FCT), which are funded by the FAA and operated by contract personnel.
NFCTs, on the other hand, are usually funded by the local airport authority.  Some examples (not authoritative or all inclusive): Mojave (MHV), Laughlin/Bullhead City (IFP), and Merritt-Titusville (COI).
Unfortunately, there isn't a consolidated list of all NFCTs.  Rather, they are tracked by their respective FAA region.  Here are the Southern and Western-Pacific Hub Organization Orders that list their respective NFCTs (not sure if they're current).
Operation of NFCTs is covered by AC 90-93b.

The FAA has a Contract Tower program for some airports. The government pays for them and the FAA has oversight in their operation.
I know when the FAA was going to close a bunch of towers, some airports were considering funding the towers themselves. Based on that, I think the answer is yes, they can fund their own and it will have the same authority as any other tower.
More information is also here and here.


text:
How do I use the FAA's WINGS program as a flight review?
I know pilots can substitute WINGS phases for the Flight Review otherwise required every two years. How do I do this? Do I have to attend a class to meet all the equivalency requirements?

The FAA Safety Team's WINGS program allows pilots to bypass the traditional FAR 61.56 flight review by completing a "phase" of the WINGS program.  The program and requirements are detailed in FAA Advisory Circular 61-91 (currently 61-91J).
The short version is that a "phase" of WINGS consists of three credits of "flight activities" and three credits of "knowledge activities", which must be earned with a 12 calendar month period.
Flight credits are earned by flying with an instructor and demonstrating safe & proficient flying skills in specific areas of operation.
For example, one "Basic WINGS" flight activity (worth 1 credit) is demonstrating basic air work - forward slips, steep turns, rectangular course, S-turns, and turns around a point - to Private Pilot practical test standards.
When you have successfully completed a flight activity your instructor can log in to the FAA Safety / WINGS site and give you credit for completing the activity.
Knowledge credits are earned by attending seminars and classes - these can be in-person seminars set up by the FAA Safety Team, or on-line webinars.  Many of the AOPA Air Safety Institute online courses qualify for WINGS credit.
When you complete a phase of wings your flight review clock resets, and your flight review becomes due 24 calendar months from the date you completed that phase.

Ultimately participating in the WINGS program probably means you will be spending more than the "bare minimum" 1 hour of ground time and 1 hour of flight time that FAR 61.56 requires. While you can often complete flight activities in an hour (or much less if you're proficient) the knowledge topics often take longer: the webinars are typically 30-40 minutes each, and in-person seminars can easily last an hour or more.
The major benefit to the WINGS program is increased safety through building your knowledge and proficiency - the seminars are actually informative (and the in-person ones can even be fun, depending on who is running them), and the flight activities are pretty easy (though there are certainly challenging ones available if you want to push yourself and really sharpen your skills). Resetting the flight review is an enticement to encourage all of us to participate.


text:
What is this extension/device on top of the wing of this ultralight?
This a shot of the Aero Synergie Papango ultralight, the succesor of the Aero Synergie J300 Joker.

The wings are more elaborate compared to its predecessor's and include on their top two additional extensions/devices.
What are they? Any aerodynamic role or just for aesthetic sake?

Those are wing fences and they prevent airflow perpendicular to the direction of travel. This isolates the portions of the wing and allows the inner wing to stall independently of the outer wing.
Since the wing uses flaps, the inner portion will create more lift and stall (separation of airflow on the upper wing leading to loss of lift) at a lower angle of attack. Wing fences prevent this stall from extending over the outer part with the ailerons, so the airplane will stay controllable in a stall and will not suddenly drop one wing.

Why is that a benefit?

@GrahamBorland it is more beneficial for swept wings, but because the isobars don't need to be in line along the whole wing you can get away with more

I must be missing something - wings can stall? I thought engines stalled... How can part of a wing stall when the rest of the craft hasn't? Aren't they all travelling at the same speed? Or is that something that kind of deserves its own question...

@corsiKa when a wing loses lift that is called stalling, and the different aerodynamic properties of where the flaps and ailerons are is enough to provide different stall characteristics

@corsiKa: See http://en.wikipedia.org/wiki/Stall_%28fluid_mechanics%29

@corsiKa: Most wings are slightly twisted to make the stall progress gradually from the middle outward, keeping the ailerons effective longer and generally give pilot more time to react. And the wing fences slow the stall a bit more.


text:
What regulations in the US exist for jetpacks?
In 2010 Fox News posted an article in which they quoted a representative of the FAA saying that the FAA might not regulate jetpacks (the representative did say that they could fall under Part 103). Do any regulations exist in the US for jetpacks?

If they don't regulate them, then I guess the answer is no?

The article, and I think the FAA rep, actually suggests that they very well might fall under Part 103 (ultralights).

Right, the answer would be "No, none exist." It may be that no one can find any sort of reference to regulation of jetpacks other than that previous statement by the FAA. I'm fine with that answer; I'm just trying to see if jetpacks fit into some regulation somewhere.

@egid Yes, but it does mention that there was some hesitation over whether to even put jetpacks under Part 103.

Another thing I'm curious about is this: If the FAA definitively said they do not regulate jetpacks, would a jetpack user (in theory) be allowed to fly in any airspace (except maybe TFR)?

@called2voyage I bet you'd still be shot down.

@PatoSáinz Obviously, thus the "in theory" part.

Someone apparently was flying a jetpack in the Class B airspace around LAX last weekend and the FBI has gotten involved. If someone actually got up to 3000 feet then today's jetpacks are significantly more capable then those of 10 years ago. Apparently this is being considered a flight...

@MichaelHampton Might need a new answer then!

This depends on what you mean by a "jetpack". If you mean the classic James Bond-style rocket pack, then according to an FAA spokesman quoted in the Wall Street Journal they just don't fly long enough for the FAA to be interested:

Once aloft, a jetpack pilot is preoccupied with getting down quickly:
  A typical pack holds about 10 gallons of fuel, only enough to fly for
  about half a minute. The Federal Aviation Administration doesn't
  regulate jetpacks. "Thirty seconds is not sufficient to be considered
  a flight," says FAA spokesman Les Dorr. He adds that it's up to the
  individual to assess the risks.

On the other hand if you're referring to the Martin Jetpack, which uses fans instead of rockets, then several sources (e.g. Wikipedia) say that it's considered an ultralight by the FAA, in which case all the usual ultralight regulations would apply. But I couldn't find any direct confirmation of that on Martin's site.

Sounds about like what I would expect, thanks.

Thirty seconds is not sufficient to be considered a flight . . . Sorry Orville! :-)


text:
During a takeoff emergency, is it safer to abort or continue the takeoff if either can be done within the available runway?
In a multi-engine airplane, if an engine failure occurs at the exact moment that a decision needs to be made to reject or continue the takeoff, and there is plenty of runway available to do either, which one is statistically safer?
A more technical way to ask the same question would be:  When there is sufficient runway available, is it better to artificially increase $V_1$ (via an assumed temperature takeoff or similar approved procedure) in order to stay on the runway longer in case an abort is required, or would it be better to leave $V_1$ at the lower speed and take any problems into the air?

I don't know about the statistics (I don't think there are that many for that scenario), but you know the saying: in case of doubt: I'd much rather be on the ground wishing I was in the air then being in the air wishing I was on the ground.

@PhilippeLeybaert While that is true, I've also seen some spectacularly bad high speed aborts that could have safely taken off and come back for a more "normal" landing....

You specifically assumed that there's plenty of runway available. If it's plenty, an abort shouldn't go bad in a spectacular way I guess. (please forgive my oversimplification of the issue, I'm not an expert)

@PhilippeLeybaert You're right.  It shouldn't but pilots don't have the best record when it comes to high speed aborts either.  That's why I'm wondering which is actually statistically safer.

If they're not good at high speed aborts they're probably not good at handling an engine-out takeoff as well :-) But I'll shut up now and leave it to the experts...

If such a situation arises in the real world, you don't have time to post to StackExchange and wait for an answer.  In truth, the decision has to be made before you enter the runway, then the only thing to do is execute the plan.  If you called V1, you continue the takeoff.  If you have not called it, you abort TO.  The safest course comes in acting decisively.

@abelenky Absolutely!  My question centers on the  different philosophies used to determe V1 though.

What is waiting for you at the end of the runway? Is it a nice green pasture or a 3000' drop straight into the ocean?

@Radu094 Well, with "plenty of runway" to do either, it shouldn't matter!

@abelenky leaves a fraction of a second where it could happen. PNF calls V1, and at that precise moment there's a bird strike of tyre failure... Shows how slim the chances of it happening are.

from my understanding the training and procedures make this kind of armchair decision making moot.  Abort takeoff until you can no longer abort and the delineation is clear to all in the cockpit - at least it should be based on my understanding of training and procedures.  I would imagine that statistically, the best chance of good outcome is to follow the training you have had.

@tim This is a question meant to get the information which can be used to create the training and procedures, hopefully drawing from an answer based on actual statistical information about high speed aborts. In any case, you make it sound like you think that learning about what happens in this situation is a bad thing?

@abelenky: If you called V-1, you continue the takeoff if the aircraft is still able to fly.  Important distinction there.

In my experience, admittedly dated (retired 1999) whether it's 'better' or not didn't enter into the consideration. A reduced-power assumed-temperature was always used (unless there was something that prohibited it) because of the cost factor, and the power reduction used was always such that there was the proper amount of runway but not 'plenty' of runway. There was a maximum amount of reduction above which you could not legally go, but that was rarely used in my experience.
All that said, it's the captain's airplane. While I was a 747 f.o., I occasionally saw captains use less than the power reduction called for. More often, but still not a lot, I saw captains simply call for a max power takeoff rather fussing with adjusting the reduced power. Max power takeoffs were always entered into the aircraft maintenance log because it was required to do one every so often. I forget the exact requirement..
When I was a captain, I almost always observed the recommended reduced power. Twice doing this it became a closer thing than I would have liked. The first time was on the reef runway at Honolulu. We were over 800,000 lbs, it was my leg, and we lifted off at the very end. I rotated a couple of knots or so early because the end seemed to be getting very close. I thought a lot about that takeoff and discussed it with a number of people. My view, and I think the consensus view was: beware of high-humidity reduced power takeoffs. Humid air is less dense than dry air, but the performance charts (at least the ones we used) didn't take that into account.
A year or so later at Dhahran, Saudi Arabia, we were bringing a full load of troops back from Desert Storm. Reduced power was called for, the humidity was very high, and it was the f.o.s leg. A little over half way down the runway I didn't like how it was looking, and called for max power. Discussing it later with the f.o. and the f.e., we had all come to the same conclusion at about the same time. I had simply been the first to verbalize.

The best answer I can provide is it depends.
For an emergency involving flight controls, trim runaways, pitch trim fail, full hydraulic failure, or a windshear indication, if the remaining runway was what I knew I could land and rollout on, I would abort the takeoff.
For all other emergencies including engine failure and/or fire, I would takeoff.
That is how I briefed my FO when I was a captain and similar to how my captains briefed me when I was an FO.  The most common verbiage other captains used was "I'll abort after $V_1$ for failure to fly", and I consider the specific scenarios I mention to meet that criteria for the EMB-145.
I'll also explicitly say that I consider the aborts I listed to be safer than to takeoff:

flight controls - for obvious reasons
trim runaways - an out of trim transport category airplane can be a beast to fly
pitch trim fail - in the EMB-145 a re-trim from "8 up" to "6 up" has to happen at pretty slow airspeeds after takeoff or the aerodynamic forces on the stab will overcome the trim motor.
full hydraulic failure - we did it in the sim and it is a two person job to manhandle the controls, not particularly fun.
windshear indication - low and slow and performance decreasing windshear means you'll probably be back on the ground anyway.

I would consider aborting, given a long enough runway, to be safer than taking off for these scenarios.

Well, my question is specifically about calculating a higher V1 (which we know is safe to abort at).  While this is a good brief/procedure, it doesn't answer the question that I'm asking.  :)

Ah, I way be guilty of mainly reading the title of skimming the question.  The primary implication of increasing V1 and aborting is going to be brake performance and in particular, break overheating and fire. So I don't know that I would arbitrarily adjust it.

Well, I'm not suggesting arbitrarily adjusting it (which is why I said to use an assumed temp or similar approved procedure).  :-)

Yes, I see that now.  We always did reduced thrust takeoffs when able, so we were already at the highest published V1 for weight and configuration.

As an example of a successful abort after V1 for failure to fly, see this AvHerald link where a Chautauqua E135 aborted at Vr after their elevators came undone when trying to take off from JFK.

@UnrecognizedFallingObject: And here's an example of an unsuccessful abort after V1 for failure to fly.

Well, since you are asking about 'statistically' :
I have a Boeing presentation entitled 'V1 and the Go / No Go Decision' from 2002
In there it presents the case of Rejected TakeOffs and Overruns out of an estimated 76,000 RTOs studied between 1958 and 1990 about 74 ended in Overruns. 56% of them were initiated after V1 (most of them >120kts), and also 56% of them were avoidable completely by continuing the takeoff.
This puts your statistical chances of a mishap about 0.1% in case of RTO before V1 and about 56% after. If you think you have a better chance in the air, take the flight.

I would expect aborting after V1 (especially > 120kts) to be more dangerous!  :)  I'd love to see a speed (relative to V1) -vs- accident rate graph.  That would provide some insight on the issue, but runway distance remaining would also be a factor.

I'd guess the reason for the abort is also a factor. If 56% of the post V1 aborts were due to trouble that ended up inhibiting braking...

While things can certainly go wrong on the ground, there are more things that can go wronger faster and worser in the air.

In light airplanes, if you have runway remaining, landing is the preferred choice even once you've taken off.  It's not a "ground reject or continue" choice.  It's a 3 stage process.

Can I reject safely on the ground?
After that point, Can I now land safely in the remaining distance (or even have a survivable runoff, which you may choose if you know your particular airplane can't climb on remaining engines)
After that, I'm committed to lost engine procedures and attempting to fly (in some configurations, sustained flight is not possible and you're actually committing to an off airport landing)

It helps if you have a retractable gear: you can use the retraction of the gear as the switch between the two, much like V1 does for big a/c

I'd clarify that to say that "gear up" is your switch between option 2 and 3.  The switch between option 1 and 2 is leaving the ground.

authors: Bob Jarvis - Слава Україні


text:
Why is full carb heat recommended when reducing power below normal setting?
In my first flight lesson today, my instructor asked me to apply full carburetor heat when we had to reduce power to 1900 RPM in our Cessna 152.
I was surprised by this as I didn't remember learning this in ground school, and I later checked the Jeppesen textbook I am using, and referring to the section on carburetor icing, I saw that when power is reduced below normal operating limits, full carb heat is recommended (must have missed it when studying the ground material).
My understanding is that the cause of carb icing is the sudden drop in temperature in the venturi due to drop in pressure as the fuel speeds up. If I am reducing power, I am reducing fuel flow, so shouldn't this reduce the chances of icing? So my question is why is full carb heat recommended when decreasing power below normal operation?

relaxing the throttle might result in a reduction in engine-generated ambient heat as well.

You might want to read the answers and comments to this question which is related.

Icing comes from the moisture in the air being drawn into the carb, not from the fuel.

Not enough time for a full answer but: fuel is a liquid with a much higher specific heat capacity, thus it has "more energy" per temperature then air. When you have more fuel flowing into your engine, the fuel heats up the air, reducing carb icing. Less fuel doesn't heat up the air as much, thus you need carb heat

As power is reduced, so is the manifold pressure, therefore there is a greater pressure drop across the butterfly (more suck) which results in a temperature drop and lowering the dew point.  As temperature drops, the moisture in the air will condense out.

reduced below normal operating limits. the only "normal operating limit" is redline

At full throttle, manifold pressure is high, close to ambient pressure at that altitude.  At partial throttle or at idle, manifold pressure is low.  It is the transition from higher pressure (ambient) to low pressure (in the induction manifold) that causes cooling.  Think of why ambient temperature is cooler at 10,000 feet MSL than it is at 1,000 MSL.  So moving the throttle to a lower power position will cool the carburetor.
The advice is right, follow the instructions in the POH.

When you close the throttle for descent, the airflow is constricted.  This constriction is going to cool the air more than it is during cruise configuration, and may increase icing.
From This AOPA document:

Throttle ice is formed at or near a partly closed throttle valve. The water vapor in the induction air condenses and freezes due to the venturi effect cooling as the air passes the. throttle valve.

At lower power settings in particular, the butterfly valve of the throttle has a smaller opening, which effectively act as venturi, making the carby more conducive to icing.

The other answers are good, but I'll contribute the physical reason.
When a gas is expanding due to pressure differences, the temperature of the gas will drop. This is stated in the Ideal Gas Law. While air is not an ideal gas, it's close enough that we can use the law to calculate the temperature drop - within reasonable limits.
PV=nRT, where P is pressure, V is volume, n is number of moles of gas, R is the ideal gas constant (8.314 J⋅mol−1⋅K) and T is temperature in Kelvin.
When you close the throttle, pressure in the manifold will drop, and the air entering from ambient pressure to manifold will have to expand. This cools it down - and as it cools it can hold less moisture as well, so you risk water vapor condensing out of the air, and potentially very cold air.

I learned that applying carb-heat when throttling down has nothing to do with Carb-Icing, but instead is to prevent shock-cooling.
When the engine is running at full power, it is creating a lot of heat.
When you throttle down rapidly, suddenly much less heat is being generated, but the engine is still being rapidly cooled.  This rapid cooling can create stress as the metal parts of the engine contract at different rates.
Applying Carb-heat directs available heat into the carburetor, and by association, the overall engine, which slows down the cooling of the engine and reduce the stress from rapid cooling.

Carb heat may or may not help with shock-cooling, but even if does, 1.) I suspect there are limits to how much it can help and 2.) shock cooling is not generally a huge concern (though a good pilot will always be mindful of it and do everything practical to reduce even that slim possibility) in aircraft with smaller and non-high performance engines. Effectively preventing shock cooling requires closing the cowl flaps (if installed and currently open) and ensuring that throttle reductions are both smooth and gentle (don't want to say slow lest someone assume 1" of M.P. reduction per hour :P )

@abelensky: You need to ask your instructor who told you that carb heat is used to prevent shock cooling for a reference to any legitimate source that backs up this statement.  Please post it here.  I strongly don't believe that carb heat is useful in reducing shock cooling, but hey, we are all always learning, right?

The final authority on the use of carb heat is the POH, unless the POH itself leaves it to the pilot to make a judgement call, in which case you have to reference your knowledge of carb icing formation, the specifics of the aircraft's system, your intended operating parameters, and current atmospheric conditions.
Your instructor asking you to use carb heat when reducing power is likely both in line with the POH (can't remember for certain, it's been years since I've seen a -152 POH) as well as general prudence when operating carbureted aircraft, especially something with an engine that small.

Very true, although I think that "pilots discretion" is unlikely and potentially dangerous.  I was taught POH and keep the carb gauge in the green which was above (from memory) 15c and below -2c and at all times in the the final descent or sustained low power.  The point being that adding carb heat can cause icing if not used properly.

Simon, two points:  First, very few Cessna 152s have a carburetor temperature gauge.  It was optional equipment coming out of the factory.  Second, adding heat can cause icing?  Well, no but there is a dangerous truth to what you say.  Using partial carb heat can melt ice, with the water flowing further into the induction system where it can refreeze.  From this point full carb heat will not melt it.  So use full carb heat if you suspect ice.  If you do have a carb temp gauge, then and only then is it safe to use partial carb heat.

@Simon There are quite a few POH's out there that will have something to the effect of "only use carb heat if icing is suspected to be a concern". This was, to give but one example, the case with the Lycoming-powered Husky I've flown for both work and pleasure around Florida for several years. You are correct that "pilot's discretion" can be dangerous when used improperly, but, with proper knowledge and understanding of the factors involved (and a healthy dose of operational conservatism), it often makes the difference between efficient execution and simple resource and performance waste.

@SkipMiller  Adding heat in very low temperatures can indeed induce icing.  Start here http://www.pprune.org/archive/index.php/t-218441.html


text:
How to find the location of the Aerodynamic centre?
Everywhere I look I'm only able to find information about airfoils.
How do I find out the location of the Aerodynamic centre of an arbitrary aircraft irrespective of its type or shape?

Do you mean center of lift perhaps?  Or center of gravity?  There can't really be an aerodynamic center because aerodynamics is a reference to flow not force.

@JayCarr From Wikipedia: "The aerodynamic center is the point at which the pitching moment coefficient for the airfoil does not vary with lift coefficient (i.e. angle of attack), so this choice makes analysis simpler." I personally had never heard of the term and was surprised to find so much on it when I Googled "aerodynamic center." Live and learn, or maybe in my case live, learn, forget, learn again?

@Terry or!  Or I could be wrong!  lol, not the first time, probably not the last.  I should have just google it like you, this is what I get for being lazy ;).

@Gaurang are you talking about how you could find it for an arbitrary aircraft or a specific aircraft like the Boeing 737?

Yes.A method for any arbitrary aircraft irrespective of its type or shape.

Aerodynamic  is everywhere: Find out here how BMW aerodynamic test center carry out optimisation of the car’s aerodynamic qualities. Wind tunnel is the mantra...

@menjaraz if you have the money for it :P Otherwise simulation is. (and is anyway before the wind tunnel)

@Frederico: Indeed, simulation is the way to go. Nevertheless simulation or not, one has to be good at CFD prior to playing/harnessing them. I know of an amateur built wood and fabrics ultralight designed using homemade wind tunnel.

@menjaraz ["Federico", no 'r' after the 'F', or I will not get notifications ;) ] Yes, you can also use a homemade windtunnel, but your observation about CFD stands also for wind tunnels.

@Federico: Sorry for the misspelling. Is there an opensource library you recommend (modelisation/simulation)?

@menjaraz for CFD? I would not know. In an answer XFoil was suggested for wings, but I do not know for full bodies. I think you should better ask Peter Kämpf.

@Federico: That would be for sure computationally intensive - Another layer of complexity...

You can find out where the aerodynamic centre is during a flight test. Are you looking for the procedure to do so?

What you refer to as the aerodynamic centre is also called the neutral point, the point where pitch moments do not change at all angles of attack with attached airflow.
If you ask for an unswept body of high aspect ratio, the answer would be easy: At the quarter chord point in subsonic flow and at the half chord point in supersonic flow. Unfortunately, the neutral point shifts forward with decreasing aspect ratio until it sits right at the leading point (not edge) of a slender body, a body with infinitesimally small aspect ratio. It shifts slightly backwards with positive sweep, so you normally have to calculate correction factors which depend on

Sweep angle
Taper ratio
Ratio of fuselage width and span
Lengthwise position of the wing-fuselage intersection
High wing or low wing configuration (negligible influence)

If you don't have good wind tunnel data or a validated CFD model, you would use a collection of formulas and diagrams like DATCOM (see this link for a computerized version) to approximate a solution. Sorry, but I cannot give you a simple formula which would work out of the box.

Can't you use the stability derivation?

Differentiate to $\alpha$
$$
\begin{eqnarray}
\frac{\text{d}C_m}{\text{d}\alpha} &=& 0 + \frac{\text{d}C_L}{\text{d}\alpha} \frac{l_{cg}}{c} - V_H\frac{\text{d}C_{L_H} } {\text{d}\alpha} \\ & &\\
 &=& \frac{\text{d}C_L}{\text{d}\alpha} \frac{l_{cg}}{c} - V_H \frac{\text{d}C_{L_H} } {\text{d}\alpha_H} \frac{\text{d}\alpha_H } {\text{d}\alpha}
\end{eqnarray}$$
Resulting in:
$$ C_{m_\alpha}  =  C_{L_\alpha}  \frac{l_{cg}}{c} - V_H C_{L_{H_\alpha}}  \left( 1-\frac{\text{d}\epsilon}{\text{d}\alpha} \right)
$$

Hi Luca, and welcome here! May I suggest that you use MathJax to improve the readability of your answer? Also see here for general info on how to edit an answer properly. BTW, no downvote from me. I think the two who did were rude.

Hello Luca, also welcome from me. Like Peter suggested, I would encourage you to use MathJax to improve the readability of formulas. It may seem difficult to begin with, but once you get the hang of it, it's easy to use. To help you get started, I've converted the first couple of formula's from the second half of your answer to MathJax for you. You can see the code when you edit your answer. Good luck in converting the rest. If you need help, just ping (by adding an @ in front of my name in a comment to this answer)

@PeterKämpf: I didn't downvote either but this answer (longitudinal stability) has actually nothing to do (at least not directly) with the question (aerodynamic centre). I think is the task of who wrote this answer to highlight the link between the two concepts.

@sophit I never tried to decipher the writings.


text:
How to make use of linear acceleration and gyroscope data?
This is strictly not aviation related so please feel free to move it to the correct section.
I have a 9 axis IMU, which gives me yaw, pitch, roll, magnetics, gyros, accels etc.
I currently make use of the roll, pitch and yaw (true) however I want to learn how to use the rest of the data. I know that the raw magnetometer data can be used to judge when the true yaw is not accurate enough and even correct it. I'm reading up more on that subject at the moment.
However what I can't find much resources on is on how to make use of linear acceleration and angular acceleration. I have successfully converted the data from raw units to g/s.
How do I obtain the acceleration of my craft with the data?

Sounds like rocket science!? Maybe a good fit for Space Exploration or Physics

@menjaraz: Inertial navigation is used in aviation just as much (or more) than space exploration. If the desired answer is expected to have some equations, Physics would be a better place indeed.

@jan-hudec: Good point, I stand corrected :-)

You integrate accelerations to get speed and integrate speed to get position. So if you have angular speeds or even orientation, I don't see any use for angular accelerations. That does not mean the unit does not use them internally when calculating the angular speeds and/or orientation.
The linear accelerations can be used for dead reckoning. Airliners, and increasingly any plane with glass cockpit, have inertial navigation system that integrates the accelerometer and gyroscope data to keep track of position. It used to be primary means of navigation over ocean before GPS and now it is still used as backup if GPS signal is lost and for compensating errors by cross-referencing.
The lateral acceleration is also shown by the slip-skid indicator (used to be accompanied by turn rate in turn indicator, but glass cockpits often only have attitude indicator provided it is non-tumbling and maintains precision at unusual attitudes; see also When/How may I replace the Turn Coordinator with an Artificial Horizon?).

I don't think that normal discrete integration will work? Because of all the noise that will come into play?

@spaghetti-: It is digital, so it is necessarily discrete integration. Of course it's not just adding numbers. Numerics folks have various methods for filtering out noise (usually Kalman filters; may be already implemented in the unit) and interpolating smooth curve through the data points and integrating that to increase the precision (best known are probably Runge-Kutta methods). I haven't done much numerics myself so I don't know what exactly would be used or how to tune it.


text:
Why do planes make landing approaches at significantly varying heights?
I live in NYC and my house is under one of the approaches for JFK. Im still about 15 miles away from JFK, so the noise isn't an issue 99% of the time. Once in a while however, especially if I'm outside, I notice that the plane is much louder and seems to be visibly lower.
Why is this? I'd figure with all the fancy GPS and radar systems planes and ATC have that the landings would be near identical, but this doesn't seem to be the case.

This post shed some light on stabilized approach: some details related to recommended height provided.

Unfortunately, since I don't know your particular location relative to the airport, I can only give some general answers as to why this might be.
Contrary to popular belief, the availability of precision approaches does not mean they are used 100% of the time, nor are aircraft always routed the same way. Depending on the airport, the use of precision approaches can drastically reduce the number of aircraft that can be handled in a given period of time.  As such, during visual meteorological conditions, flights will almost always be cleared for a visual approach. Busy airports will typically have a number of standard arrival routes (STARs) that make the approach routing consistent and predictable (which could explain why noise is not an issue 99% of the time), but pilots are not obligated to use them.  If a STAR is not used during a visual approach to an airport with approach control services (like JFK):

The approach controller (using radar) will direct the plane in such a way to allow the pilot to visually acquire the runway, at which point the controller will clear the pilot for a visual approach. Additionally, under radar vectoring, the aircraft may be told to fly a particular heading for sequencing and/or spacing which can vary due to the amount and type of traffic.
Once cleared for the visual approach, the particular approach course and altitude is at the pilot's discretion.

The situation is similar for an instrument approach, except that the approach controller will arrange to have the aircraft either navigate to an initial approach fix on a published approach procedure or vectored to intercept the localizer before clearing the pilot for the approach.
Sometimes, unusual flight paths can also occur when a runway that is not normally used for landings is made active.  This can happen when wind favors a particular runway, or the one that is normally used is taken out of service (e.g. maintenance or an accident).


text:
What is the history of glass cockpits?
All glass cockpits seem to have the same basic setup for the primary instruments. Altitude tape on the right, air speed tape on the left, turn coordinator on top and an artificial horizon in the background. I can't find any good information on how the glass cockpit came to be and more specifically, how this layout was developed and adopted. I'm curious about:

Who developed the first glass cockpits?
Which planes first used these glass cockpits?
How was the current layout developed, were other layouts in use beforehand?
Was there any resistance or difficulty in getting these systems adopted amongst pilots or their companies?

I ran across this interesting paper while researching something else, it has some interesting info about the design considerations for electronic displays.

And why are they called glass cockpits? Even the old analogue dials all had glass covers on them.

It depends on how you define "glass cockpit." Technology has progressed in steps to the modern "glass cockpits" of the latest aircraft.

Who developed the first glass cockpits?

The military appears to be the first place where electronic displays were used. First for specific uses like navigation or targeting scopes, and later gaining more functionality.

Which planes first used these glass cockpits?

The Blackburn Buccaneer was the first production aircraft with a HUD and entered service in 1963. The North American F-111D was equipped with a multifunction display and entered service in 1970.
The commercial side of the industry took a bit longer to adopt the technology.
The McDonnell Douglas MD-80 had a glass primary flight display and navigation display, and entered service in 1980.
Boeing started work on glass cockpits in the 1970s while developing the the Supersonic Transport (SST). While the SST never entered production, the work on glass cockpit technology was used in the design of the 767 and 757, entering service in 1982 and 1983, respectively. This was based on work with NASA, including testing on a 737 aircraft beginning in 1973.
The Airbus A310 entered service in 1983, and also used glass cockpit technology. The A320, entering service in 1988, was the first aircraft regarded as having a "full" glass cockpit, replacing traditional instruments for the primary flight instruments.

How was the current layout developed, were other layouts in use beforehand?

The first displays were generally dedicated to specific functions. For commercial aircraft, there was a primary flight display (PFD) showing the pitch and roll of the aircraft. There was also a second display for navigation which displayed the aircraft's heading.
As RedGrittyBrick points out, adding the speed and altitude to the PFD was natural due to their typical position on either side of the PFD. The use of the vertical "tape" format allows the same visual sense of direction as a round dial while taking up less space in the display.

Was there any resistance or difficulty in getting these systems adopted amongst pilots or their companies?

Although there was certainly a sense of caution with the introduction of new technology replacing the most important instruments in the cockpit, the benefits were enough to get the changes adopted. Here is a study from 1989, focusing on the "glass cockpit" in the 757. It covers the effect on the pilots and their opinions of the new technology.
The study shows that the pilots had an overall positive view of the new technology, since it reduced their workload and made tasks easier in many situations. However, the report also identified issues with crew members becoming "complacent" due to more automation, and some tasks actually became more difficult with the new systems. There is also the issue of training pilots on the complex new systems, and about what information should be hidden from pilots either during training or in operation of the aircraft. These types of discussions are certainly not going away, as is evidenced by recent events.

The first production airplane with a HUD, according to Wikipedia, was the Blackburn Buccaneer in 1958.

@egid it looks like HUD already existed during WWII here on a P51D

@ManuH, that's a reflector sight, not a HUD.

I can't find any good information on ... how this layout was developed

The glass cockpit arrangement for the primary flight display copies the defacto standard analog instrument minimal T arrangement that pilots are/were used to.
Airspeed     Attitude   Altimeter        Airspeed       Attitude     Altimeter

 .........
              Heading                                  Heading

From Wikipedia

Electronic displays had been used extensively in military aircraft since the 1960s, but I believe NASA Langley with their Terminal Configured Vehicle program was most directly responsible for the initial research of electronic flight displays in commercial aircraft. Starting in 1973, they used a modified Boeing 737 to begin research into using computer displays on commercial aircraft.
Starting on page 36, this history of the 737 flying lab, goes into great detail of their research on electronic flight decks.


text:
Has the cause of the engine failure of Cessna's 182JT-A been determined?
Last August during a certification flight, a Cessna 182JT-A compression-ignition (diesel) engine failed in flight. I've been Googling to find the cause of the failure and the status of the certification process but have failed to find any recent info. Does anyone know what the current findings have been and how Cessna expects to proceed?

Apparently, yes, it has -- see Cessna 182 JT-A Certification 'Imminent'.  As the article reports, the issues appeared to be related to the turbocharger, but I'm not sure how far (if at all) accident reports or details go beyond that.


text:
Why don't all new GA planes include a parachute system?
When the Cirrus was first introduced, it included a Ballistic Recovery System, which shoots a parachute out the rear of the plane that can save a plane and its occupants when something goes wrong.
Seeing as how this technology has been honed over the past decades, why don't all new planes incorporate this feature?  I would think that any drawbacks outweigh the benefit of not losing one's life when something happens unexpectedly.

I'd venture a guess to say that the manufacturers have to do a cost-benefit-analysis to see if they think that they will gain enough additional sales to offset the additional cost to incorporate and certify such a system.  We have a supply-demand market, and if people keep buying airplanes without parachutes, they will keep making them!

Remember that a lot of "new" GA planes aren't that new -- you can buy a new 2014 Piper Archer (PA28-181), but that aircraft's design is largely unchanged from the first PA28-181 certificated in 1975 (same wing, mostly the same fuselage - slightly different engine & modernized avionics are the major differences). They just keep on producing that same approved design (which doesn't include a parachute)...

@voretaq7 I understand that, and realize that certifying a new airframe is millions of dollars.  I just figure certain upgrades are worth it in sales and safety record.

I disagree with the statement that it "can save a plane".   My understanding is that the moment the parachute is deployed, the plane is considered a total loss.  Everything is designed to save the people, generally at the expense of the plane.  The landing gear, structure, frame, etc, all crumple and collapse to absorb energy and protect people.

Even with parachutes, MANY Cirrus airplanes have crashed.  The most dangerous parts of any flight are at exactly the times when a parachute cannot be, or will not be, effectively deployed (eg. takeoff, landing, and CFIT)

Also, the additional weight of the parachute would reduce the payload of the aircraft, creating incentives to overload aircraft with such devices more than they already do (along with all the side effects, such as increased stall speed, higher parachute sink rate, etc.)

@abelenky At least on Cirrus aircraft deploying the chute doesn't in and of itself mean that the aircraft will be a total loss. It is an expensive action to be sure - the landing gear may fail, and the parachute mechanism (and panels it blasts through) will need to be replaced - but absent any other serious problems that lead to you deploying the chute (like say losing a wing due to ill-advised aerobatics) the aircraft can still be repaired to an airworthy condition at a relatively reasonable cost.

Just as a side note, in Germany, I think fixed wing, powered, aircraft (with elevator, rudder and ailerons) in the so called UL category (MTOW up to 472.5 kg, most of them qualify as LSA in the US) are required to have a parachute.

Airframe parachutes are becoming an increasingly popular option on newly-certificated aircraft, thanks in part to the track record of successful deployments on Cirrus aircraft.
If I had to speculate on why they're not showing up in older certificated designs (like the Piper PA-28 or the Cessna 172 & 182) I'd go with the reason I mentioned in my comment: "New" Pipers and Cessnas are basically extended manufacturing runs of very old designs - going on 50+ years. Changing an existing aircraft design to include the required hardpoints, breakaway panels, etc. for a parachute system would be a substantial change to the type certificate, and under Part 23 certification rules doing so would cost the manufacturer an equally-substantial sum of money for the design, engineering, and testing required.
Light GA aircraft sales at the moment are, shall we say, lackluster -- the additional costs for the engineering, the type certificate update, and the parachute itself would certainly not help matters, as that cost would need to be passed along to the eventual purchaser of parachute-equipped aircraft (which would probably mean putting a 50+ year old classic Piper or Cessna design in the same price category as a clean-sheet Cirrus SR20/SR22).
In addition to the mainly-financial reasons above Quantas 94 Heavy has a point regarding weight.  BRS (the premier airframe parachute company) makes a STC'd kit for some Cessna aircraft.
This kit costs about 80 pounds of useful load, and on many light GA aircraft the useful load is marginal enough that this added weight means you're effectively sacrificing a passenger to the installation. The Cessna retrofit kit also takes up a substantial amount of space in the baggage compartment as you can see from their installation white paper, which is certainly a negative factor as well. Were the chute to be incorporated into the design by Cessna it would likely be installed in a similar location (there just aren't many other places to put it) with a similar cost in weight and cargo space.

Although I couldn't find further references to it on the site, BRS did also have a STC for a chute for Cessna 152s available at one point. As I recall the cost in useful load was comparable to the 172/182 chutes, and doing the math on a couple of 152s I'm familiar with it would have limited you to an 80-90lb flight instructor in the right seat. Clearly that makes it a less-than-attractive option for that particular type of aircraft.

Also, Diamond's safety record beats Cirrus per flight hour, from what I last saw, and it's chute-free.

@egid I thought the airframe parachute was an excellent idea, and then someone mentioned the human factor: pilots making flights they normally wouldn't have, but in the back of their mind they go "well, I have the chute..."  I still think the chute is a good idea, but it's interesting that (like most things) it's not as simple of an idea as it seems, and people think that this is a contributing factor to the higher accident rate in Cirrus compared to Diamond (among other reasons, of course!)

@Canuk: I wouldn't think a pilot who would be unwilling to take a flight that had an X% chance of killing him would be willing to take it if it had an X% chance of destroying his airplane and an X/10% chance of killing him.  On the other hand, pilots who have less confidence in their abilities might be more inclined to take planes with a protective system than would be those who have more confidence and would be less likely to need such a system.


text:
How long after takeoff for a Boeing 747-400 to reach cruise speed?
Assume it is fully loaded (pasengers and cargo) and optimal conditions, almost no wind, etc etc...
How long after takeoff does the plane reaches cruise speed?
If he goes in a straight like on the axis of the airport strip (i.e. makes no turns), how far will have it traveled when it reaches cruise speed?

I did a search on FlightAware for 747-400 aircraft in flight, and sorted by the estimated time enroute. A Qantas flight from KLAX to YSSY came up. I'm assuming that for a 6500 Nm flight, at 13.5 hours, the aircraft is fairly heavy at takeoff.
The flight data shows a departure at 03:28:33, reaching an initial cruise level of FL300 at 03:52:59, after a continuous climb. It was at cruise speed at this point, which gives a time of 25 minutes after takeoff. Comparing the coordinates of these two reporting points gives a distance of about 180 Nm, which from the track is pretty straight.
If you just want to know when it reached a speed around that of cruise, this was about 10 minutes and 80 Nm earlier in the climb, when it reached a ground speed of about 480 knots.

DL159, a 747-400 from Detroit (KDTW) to Seoul (RKSI/ICN), appears to be similar, reaching a groundspeed of 480 kt about 15 minutes after the displayed departure time. However, it was up to 460 kt by about 12.5 minutes after departure.

The question is not precise. If you make a 80Nm flight hop between two airports you will never reach cruise speed. Example ZRH-GVA with MD11 each Monday morning (aircraft positioning).
Cruise speed may change during the flight due to unforeseen circumstances prior to take off.
Cruise altitude changes during the flight when ship gets lighter. You start FL310, you may finish the flight at FL370. Or if the wind forecast was wrong, you may decide to fly lower at a different speed.
Computers are calculating during the climb the best speed, thrust setting to climb using temperature, wind forecast, fuel price, cost of operation. So your TOC could be anywhere. If you have engine anti ice on that is changing too.
Since the question is not precise, the answer is not precise either: Make it average 2000 feet per minute and you will have your time to "cruise alt".

And, also, the question is not precise, so it can be assumed the answer does not need to be either. https://xkcd.com/386/


text:
Couldn't airplanes have more emergency exits?
Being near an emergency exit improves considerably the survival chances after an accident. Why not put one exit at every 5 rows?

Exits increase the price of the ticket?

The same reason why there aren't parachutes available for each passenger separately in an aircraft.

Money.
Doors cost (and weight) a lot more than plain aluminum panels. And the exit row on larger planes usually consumes one row of seats. So lets say we are on a 767 and take out every 6th outer row, that's 5 extra exit rows and 20 fewer paying seats, or $6,000 less per flight which quickly adds up to nearly the cost of the aircraft itself over its service life. And that's quite a lot of money for something that will very likely never be used. Remember that exit doors only help if the plane crash-lands in a mostly upright position. Severe crashes often add large exits by splitting the fuselage open, and lawn-dart mode accidents don't leave too many survivors.
The flying public has indicated that they are very interested in ticket price, but somewhat less interested in the safety factor. The current accident rates appear to be acceptable to those paying for the service.

"Lawn dart mode". Excellent!

It's also possible that more emergency exits will mean more deaths.  Adding more exits will reduce the number of passengers each plane can carry, meaning more flights and more non-survivable crashes, but fewer crashes where passengers can't exit in time.  It's unclear which very rare effect will be the deciding factor in the total number of passenger fatalities.

The flying public has indicated that they are very interested in ticket price, but somewhat less interested in the safety factor. So if I'm getting a deal on the fare, I don't care about getting to my destination? Ironically, that is true.

Btw Paul, you are contributing very nice contents here. Why haven't you registered?

@Farhan simply because the process is bothersome.

Also more doors means more door maintenance means more maintenance costs.


text:
What medications may pilots take while flying?
We all get sick, suffer from allergies and sometimes chronic issues.  It is not safe to fly while on some medicines or in some cases, for some time after taking the medicine.
How do I know what I can take and still fly?  What resources are out there to check if a specific medicine is compatible with flying (AOPA, FAA, etc)?  Is there a comprehensive list of what I can and cannot take?

AOPA has the best database that I know of, but you have to be a member to view it.  They have some free information on their Medications page though.
There they talk about FAA Policy, and it starts with:

The Federal Aviation Regulations include no specific references to
  medication usage. FAR 61.53 prohibits acting as pilot-in-command or in
  any other capacity as a required pilot flight crewmember, while that
  person:

Knows or has reason to know of any medical condition that would make the person unable to meet the requirement for the medical certificate
  necessary for the pilot operation, or:
Is taking medication or receiving other treatment for a medical condition that results in the person being unable to meet the
  requirements for the medical certificate necessary for the pilot
  operation. Further, FAR 91.17 prohibits the use of "any drug that
  affects the persons faculties in any way contrary to safety."

AMAS (Aviation Medicine Advisory Service) also has a list (which is free) but I don't think that it is organized as well.  They are recommended by ALPA and NBAA though.
The most important thing though, of course, is to self evaluate and make sure that you don't fly if you are having any adverse reactions from the medication, or the underlying condition that you are taking the medicine for.
Any list that you consult has to be used only as a guide though, and not a carte-blanche approval.  Individual people can have reactions even to medications that are considered "safe" and "allowed" by the FAA, and this is why they don't list specific medications that they allow.  The FAA has a brochure called Medications and Flying, and one part of it has a few things to consider before taking any medication:

First, consider the underlying condition  that you are treating. What
  will be the  consequences if the medication doesn’t work  or if it
  wears off before the ﬂight is over?  A good general rule to follow is
  not to ﬂy  if you must depend on the medication to  keep the ﬂight
  safe. In other words, if the  untreated condition is one that would
  prevent  safe ﬂying, then you shouldn’t ﬂy until the  condition
  improves — whether you take the  medication or not.
Second, you must consider your reaction to  the medication. There
  are two broad categories  of medication reactions. One is a unique
  reaction  based on an individual’s biological make-up.  Most people
  don’t have such reactions but  anyone can, given the right medication.
  Because  of this, you should NEVER ﬂy after taking any  medication
  that you have not taken before. It  is not until after you have taken
  the medication  that you will ﬁnd out whether you have this  uncommon
  and unexpected reaction to the  medication.
Third, consider the potential for adverse  reactions, or side
  effects — unwanted reactions  to medications. This type of reaction is
  quite common, and the manufacturer of the  medication lists these on
  the label. You MUST  carefully read all labeling. If you don’t have
  access to the label, then don’t ﬂy while using the  medication.
Look for such key words as lightheadedness,  dizziness, drowsiness, or
  visual disturbance. If  these side effects are listed or if the label
  contains  any warning about operating motor vehicles or  machinery,
  then you should not ﬂy while using  the medication.
Side effects can occur at any time, so even if  you’ve taken the same
  medication in the past  without experiencing side effects, they could
  still  occur the next time. For this reason, you must  never ﬂy after
  taking a medication with any of  the above-noted side effects.

Hehe - I'm imagining a pilot saying, "it says not to operate heavy machinery, but I'm just operating a glider!"

Call an AME. They'll answer your questions more definitively and then you'll have an official opinion. AOPA's database is good but it is not official and probably wouldn't hold up as a defense if you somehow got in trouble for using some medication that you thought was okay.
Additionally, an AME can refer you to alternative medications that might be approved. For example, Cetirizine (Zyrtec etc.) is banned because it causes drowsiness and blurred vision, but Loratadine (Claritin etc.) is acceptable. Perfectly viable substitute for some people with allergies (not me, unfortunately) but you'd never know it looking at AOPA's list (although I think AMAS talks about alternatives).

Great point about the AME.

Try this link: You type the medicine name and get an answer.  https://www.aviationmedicine.com/medication-database/

Usually, including the essential info from the linked article is a good policy, but in this case, he is pointing out an on-line resource to look up any particular drug someone may have a question about. It's pretty hard to "summarize" a database like that in a post. Voted to NOT delete, as resources like this can be valuable, even as "only" a link.

Calling an AME is the official word.  You can get a pretty good idea of what he's likely to tell you from this page at LeftSeat.com -- so if that page says that X isn't approved but Y typically is, that's probably a good starting point for where to start the discussion with a "real" doctor if you're about to be given a prescription.  (Not knocking AME's, but many pilots have the doctor they see when they're sick, separate from their AME.)
That said, nothing on the internet carries as much weight as what your AME tells you, so consider this advice worth what you paid for it!


text:
How long can passengers survive after ditching in the ocean?
Assuming Malaysia Airlines Flight 370 ditched in the ocean, and surviving passengers and crew were floating around in their inflatable vests, how long could they survive?
Is there data about the longest survival under such conditions?
There are a few examples of people surviving for months in tiny boats, but there they could gather rainwater and catch fish, obviously impossible in just a lifejacket.
Edit: although I mentioned a specific flight and lifejackets, the question is intended to be general for ditching in the ocean.

Well, they have rafts on board too.  In just a life vest it would depend on the temperature of the water, but it isn't all that long....

and assuming they ditched south of australia it would be very cold water

If you are in the water and it is below 21 C, you'll be dead within three hours. In above 27 C water, you won't die of cardiac arrest due to hypothermia. Links: 1, 2, 3. (I'm not an expert.)

I don't know where they are searching now, but you can find up-to-date surface temperatures here. (Main page.)

Well, your scenario is a bit unlikely because if the aircraft did ditch in the ocean they would have the emergency rafts and slides to take cover in instead of "floating around in their inflatable vests".
However, if someone were floating in the ocean without any protection, how long they could survive depends on various factors.  Temperature is the biggest factor in the amount of time before they would succumb to hypothermia.
Take a look at this chart to figure out the average temperature of the area in question.  If we go by the latest news, that is going to be somewhere in the neighborhood of 14C.
This page says that the Expected Time of Survival is 1 to 6 hours.
The same page also says:

Maximize your chances of surviving by:

Wearing a personal flotation device (PFD)
Adopting a survival position
Keeping clothing on
Getting as much of body out of the water as possible
Remaining still and in place UNLESS a floating object, another person, or the shore is nearby
Keeping a positive mental outlook (a will to survive really does matter)

Swimming isn't recommended unless there is little chance of being
  rescued and shore is less than a mile away. Putting on a PFD after
  falling into cold water is almost impossible – SO WEAR IT. If you find
  yourself in cold water without a PFD and nothing to climb onto, tread
  water. Traditional drown-proofing by repeatedly lowering your head
  into the water and floating speeds up heat loss.

Lots more information is available on that page!

So, in general, just lifejackets would mean a few hours in cold water, a few days in warm water, and on rafts up to a few months?

@vsz make that minutes in cold water, hours in temperate water, days in warm water. And after days you'd be dead from dehydration anyway. Rafts? Depends on weather and supplies. People have been rescued from lifeboats after 6 months, but they had means to generate fresh water, emergency food supplies, and managed to make fishing gear to procure more food from the ocean.

Well, there chances for extended survival is not exceedingly generous, according to the FARs 91.509 and 135.167. Bear in mind that it probably wouldn't take so long for a larger aircraft before they notice that it was missing.
FARs 135.167:

(a) Except where the Administrator, by amending the operations
  specifications of the certificate holder, requires the carriage of all
  or any specific items of the equipment listed below for any overwater
  operation, or, upon application of the certificate holder, the
  Administrator allows deviation for a particular extended overwater
  operation, no person may operate an aircraft in extended overwater
  operations unless it carries, installed in conspicuously marked
  locations easily accessible to the occupants if a ditching occurs, the
  following equipment:
(1) An approved life preserver equipped with an approved survivor
  locator light for each occupant of the aircraft. The life preserver
  must be easily accessible to each seated occupant.
(2) Enough approved liferafts of a rated capacity and buoyancy to
  accommodate the occupants of the aircraft.
(b) Each liferaft required by paragraph (a) of this section must be
  equipped with or contain at least the following:
(1) One approved survivor locator light.
(2) One approved pyrotechnic signaling device.
(3) Either— (i) One survival kit, appropriately equipped for the route
  to be flown; or
(ii) One canopy (for sail, sunshade, or rain catcher);
(iii) One radar reflector;
(iv) One liferaft repair kit;
(v) One bailing bucket;
(vi) One signaling mirror;
(vii) One police whistle;
(viii) One raft knife;
(ix) One CO2 bottle for emergency inflation;
(x) One inflation pump;
(xi) Two oars;
(xii) One 75-foot retaining line;
(xiii) One magnetic compass;
(xiv) One dye marker;
(xv) One flashlight having at least two size “D” cells or equivalent;
(xvi) A 2-day supply of emergency food rations supplying at least
  1,000 calories per day for each person;
(xvii) For each two persons the raft is rated to carry, two pints of
  water or one sea water desalting kit;
(xviii) One fishing kit;
(xix) One book on survival appropriate for the area in which the
  aircraft is operated.

So I'd guess the answer is around three or four days perhaps. If they got to the galley onboard within an hour before the aircraft flooded, they might have a bit more...

Useful information, but what is your guess of 3-4 days+ based upon? The current record for life raft survival is 133 days.

Well, the question specifically asks about "floating around in their lifevests", so being in the raft doesn't really apply here.


text:
Can it be determined from beyond visual range whether an unknown aircraft is armed or not?
In a typical situation, where an unknown aircraft appears on radar, and doesn't respond to any radio message, sooner or later fighter aircraft are scrambled to take a closer look.
However, can it be reliably determined whether the unknown aircraft in question is a military aircraft or a civilian one, before the pilots of the scrambled jets can take a closer look with their own eyes?
By armed I don't mean deciding whether it carries real missiles or just harmless training dummies, but whether it's a military aircraft or a civilian one. Do we know of cases when this was determined before making visual contact (assuming the UFO didn't respond to any messages)
For example, is it a fighter jet or a small private business jet? Is it an airliner or a strategic bomber? From how far can you tell the difference?

I'm not sure I have an answer to this question, but there are cases of airliners (with passengers) being shot down over mistaken identity (not all these, but some).

It depends. You're essentially asking how to obtain a positive ID. Radar can sometimes ID the a/c model, eg by counting fan blades. See also IRST (essentially a telescope) and IFF.

Sorry to edit your title but i think this way it will be draw less attention from vote-to-close people. Feel free to roll back.

Still at this time, the question should be clarified, there are interesting answers that are said to not match the question (so difficult to +1), but to me they should, unless the question is rewritten.

I'm not qualified to post an answer about this, but there are electronic countermeasure capabilities that military forces utilize that can identify various types of "things" based on electronic signatures. This could be identifying a radar's frequency, pulse repetition rate, etc., for example. It's possible to identify a specific contact (not type of contact, but the specific contact if the signature is known). I suspect this can be performed on signals that are "leaking" from the contact as well (i.e., radar turned off, but still some emissions present).

Only if the airplane wants you to know it is armed.
It has several ways at its discretion:

If it has a powerful radar, it can switch it on at altitude and announce its presence to other aircraft up to 150 km away.
It can send IFF squawks which are reserved for military aircraft. Note that IFF is used by both military and civilian aircraft.

Both methods are only indirectly indicating whether an aircraft is armed. The armament itself will not show up at BVR distances. In the end, if you want to be sure, you have to move some sensors close to the aircraft if the weapons are carried externally, or even wait until they are deployed when they are carried internally. Especially many small aircraft are used both in a civilian and a military role.
A BVR radar is a dead giveaway for a military aircraft - such equipment is not fitted with civilian aircraft, and removed or disabled when an ex-military aircraft is converted to civilian use. Similarly, supersonic speed, which can reliably be detected with Doppler radars, is a telltale sign of military aircraft approaching.
Transport aircraft are much harder to distinguish from bombers on the basis of radar signals alone, and in the end you cannot exclude that the hostile aircraft tries to spoof your equipment into classifying it as a civilian aircraft.

The question was not meant to be as specific as to identify the ammunition inside the gun of a fighter, but more about identifying the type of the aircraft. Is it a fighter jet or a small private business jet? Is it an airliner or a strategic bomber? From how far can you tell the difference?

@vsz: Depends on the weather and flight altitude. With clear skies and good binoculars maybe from 10 km (6 miles). With overcast skies only when the bombs are falling.

I wouldn't be so sure that armament, at least externally mounted armament, is undetectable outside BVR. It can have a significant affect on the radar cross-section, and while it's just a guess, I wouldn't be surprised to hear that we can even tell a bomb from a missile with certain systems (when mounted on the wing).

@BryKKan: Yes, you are right about the radar echo of external weapons. If you have a database of radar returns of hostile aircraft with all possible variation in external weapons and at all aspect angles, then yes, you can detect external weapons BVR. I think this is rather sophisticated and needs a lot of preparation.

No, this is not possible.
Imagine, FedEx flying a plane into Russia with FedEx parcels on it. A week later, the exact same plane, now hired by the US Army enters Russian airspace.
Last week, it was a civilian plane, this week, it is a military plane. The only difference is who pays the bill. How is radar going to know who pays the bill?

My question was more about identifying the type of the aircraft. Is it a fighter jet or a small private business jet? Is it an airliner or a strategic bomber?

I think you are misunderstanding the question.

@curious_cat: Actually, the more I read the OP's comments, it seems to me that he doesn't know what the question is. I should probably have voted to close as "unclear" instead of answering.

There are methods beyond the IFF itself, although what's available publicly isn't all that comprehensive.
This book on Amazon is a start; this Wikipedia article goes into more depth:

Radar offers the potential of non-cooperative target recognition (NCTR). These techniques, which could work if IFF systems fail, have been especially secret. No one has yet proposed, however, NCTR that will be effective if a coalition partner is flying the same aircraft type as the enemy, as in Desert Storm. IFF, presumably with encryption, probably is the only answer to that problem.
One open-literature study combined several pieces of radar information: cross-section, range, and Doppler measurements.[22] A 1997 Defense Department report mentions "Air Force and Navy combat identification efforts focus on noncooperative target recognition technologies, including inverse synthetic aperture radar imaging, jet engine modulation (JEM), and unintentional modulation on pulse-based specific emitters".[23]
NCTR on JEM specifically depends on the periodic rotation of the blades of a turbine, with variations caused by the geometry of the elements of the engine (e.g., multiple rotors, the cowling, exhaust, and stators). More generally, the idea of "micro-Doppler" mechanisms, from any mechanical movements in the target structure ("micro-motion dynamics"), extends the problem to cover more than rotating aircraft structures, but also automatic gait recognition of human beings.[24] The micro-Doppler idea is more general than those used in JEM alone to consider objects that have vibrational or other kinds of mechanical movement. The basisc of JEM is described in .[25][26] One non-rotational effect would be the surface vibrations of a ground vehicle, caused by the engine, which would be different for gas turbines of tanks and diesel engines of trucks. ISAR is especially useful for NCTR, since it can provide a two-dimensional map of the micromovements.

The only system designed to do this (other than the radars that Jörg mentioned that try to identify radar signatures) is IFF, which stands for Identification Friend or Foe.
The system was developed during WWII and has gone through a number of refinements. The identification is determined from the mode in which the transponder replies to interrogation. Modes 1, 2, 4 and 5 are designated for military use only. 4 and 5 are used by NATO forces. Modes A, C and S can be used for military or civilian.
The system has a lot of holes in it, though. It depends on cooperation from the aircraft to squawk the correct mode to identify itself as military. If they squawk mode A, C and S or don't squawk at all then you don't know anything for certain.
The system was part of the problem in the shootdown of Iran Air flight 655. A mistake made by the radar operator caused him to misidentify the airliner as an Iranian fighter plane.
Sometimes even visual contact doesn't help. Korean Air flight 007, a 747 was visually mistaken for a military RC-135 by a Soviet pilot and shot down.

All of the answers here do address aspects of your question, albeit from different perspectives. I think you may be missing that the finer points of the answer are probably classified and not publicly available. You're also confusing the question of whether an aircraft is armed and whether its operators intend to use it to attack you.
As Jörg and TomMcW pointed out, the specific airframe or even general type - even assuming you can reliably identify it BVR - is not necessarily an indication of its belligerent or benign intentions. Even balloons have been used in "modern" warfare. Nothing in particular (other than cost and fear of having its legitimate civilian aircraft be targeted) would prevent a hostile force from packing say, a Gulfstream G650, with explosives and using it for kamikaze style attack. No military aircraft were used in the September 11 attacks, but that didn't prevent them from causing a great deal of destruction.
The closest answer to your technical question is probably Ralph J's, but as mentioned, the details are mostly classified (for obvious reasons). That being said, identifying key characteristics of the target aircraft is definitely possible BVR (with unknown, but likely fairly high reliability). Whether those characteristics are enough to clearly differentiate a combat aircraft from a civilian aircraft really depends on how your enemy defines "combat aircraft".
As to "how far out", that's likely not going to have a simple (non-probabilistic) answer. Target identification is generally based upon a fusion of data from multiple sensors with varying operating characteristics. The specific answer almost certainly depends upon a number of variables such as terrain, weather, the size and configuration of the aircraft, its flight profile, and aspect to target.

authors: Iωάννης Μόζας